The invention relates to the manipulation of flat bodies in general, and more particularly to the ascertainment or detection of certain characteristics of flat bodies including sheets of paper, cardboard, plastic or the like (hereinafter referred to as sheets or paper sheets). Still more particularly, the invention relates to apparatus for ascertaining one or more selected characteristics of sheets.
It is often desirable or necessary to ascertain certain selected or specific characteristics (such as the length, the width, the thickness, the color and/or the quality, e.g., coarseness of edge faces) of sheets which are being processed in various machines or production lines, for example, in machines for the making of pads or other stationery products or in machines for the making and wrapping or boxing reams or other accumulations of paper sheets.
It is customary to accumulate stacks (e.g., reams) of paper sheets by severing large paper sheets or piles of overlapping large paper sheets longitudinally and transversely to arrive at sheet formats of desired size. For example, large sheets can be drawn off rolls and advanced in a predetermined direction to be severed in as well as transversely of such direction in order to obtain sheets or panels having a desired length and a desired width. As a rule, or at least in many instances, a relatively wide (large) sheet is severed by one or more rotary knives while it is being advanced lengthwise so that the wide sheet yields two or more narrower sheets or strips having a width corresponding to the desired width or length of an ultimate sheet, and such strips are thereupon severed crosswise (e.g., again by one or more rotary knives) to convert each strip into a series of discrete sheets or into a series of discrete stacks of superimposed sheets.
The width, the length and the coarseness (or smoothness) of the edges are normally considered to constitute those characteristics or criteria of sheets which are most important as concerns the quality of stacks of sheets or the quality of stationery products embodying the sheets. If the width and/or the length of a sheet departs from a desired or predetermined value, it is necessary to change the position or positions of one or more longitudinal cutters or cross cutters which determine such dimensions of the ultimate products. On the other hand, if the edges of inspected sheets are too rough, this indicates to the operator or operators that certain cutter or cutters require sharpening or replacement. Thus, the number of rejects can be reduced considerably if certain characteristics of the sheets are inspected at least from time to time in order to ensure that any departures of actual characteristics from the desirable characteristics are eliminated as expeditiously as possible.
In order to ascertain the above-enumerated and/or other characteristics of paper sheets or other types of sheets, it is customary to manually withdraw, at random intervals, samples of sheets from a flow or stream of sheets or stacks of sheets and to subject the thus withdrawn sheets to a more or less rudimentary inspection with the naked eye. For example, it is known to employ patterns or templates having the desired width and length and to compare the sizes of such patterns with those of the spot checked sheets. As concerns the quality of edges (i.e., the sharpness of the knives which are used to subdivide larger sheets or strips into sheets of desired size), the roughness of such edges is compared with the corresponding characteristic of a sample sheet; such testing is carried out by touch and/or by visually comparing the characteristics of the edge or edges of a spot checked sheet with those of the sample sheet. In many instances, the thus spot checked sheets are categorized as having qualities corresponding to those of five or more different classes or groups or categories including a top class and a number of classes of lesser caliber.
A drawback of the just outlined conventional procedures which are being resorted to in order to ascertain one or more characteristics of sheets is that the results of such tests are not reliable because they are overly dependent upon the conscientiousness as well as upon the ability of the person or persons carrying out the tests to adequately judge the selected characteristics by touch and/or visually. Consequently, when the subjective conclusions of the tester or testers are being used to adjust and/or to replace certain component parts of the sheet making and/or processing machines or production lines, the adjustments are not always likely to result in any or in sufficient improvements in the quality of sheets. Furthermore, heretofore employed manual testing is time consuming and, unless performed by a number of persons, cannot be carried out at intervals which are sufficiently frequent to avoid the making of long series of unsatisfactory sheets or stacks of sheets or products embodying unsatisfactory sheets. Thus, it is desirable to alter the heretofore known testing or quality ascertaining procedures in order to ensure that the results of tests are more reliable than those which can be arrived at by subjective examination of randomly selected sheets.